1. Field of the Invention
The invention relates to a method and device for the encoding/decoding of the power distribution at the outputs of a system. A possible application of the invention is the making of high-power transmitters such as for example those used by interrogators known as IFF (identification friend or foe) interrogators, using secondary radars.
2. Description of the Prior Art
FIG. 1 shows that the current transmission chain used in IFF transmitter structures is constituted by the following elements in the following order: a driver 1, a two-channel power divider 2, a two-channel parallel amplification device 3 having an amplifier 3xe2x80x2 and 3xe2x80x3 on each channel, a two-channel recombination device 4, a circulator 5, a two-channel switching device 6v formed by PIN diodes and a transmission device 7 formed by two transmission antennas, one sum antenna xcexa3 and one difference antenna xcex94. A switching command o(t) is applied to the signal s(t) through the output switching device 6v.
As can be seen in FIG. 2, the interrogation signal s(t) of an IFF transmitter has three pulses, the first and last pulse being sent by the antenna xcexa3 and the mid-pulse being sent by the antenna xcex94. In order to meet the requirements of the IFF ISLS (identification friend or foe interrogation side lobe suppression) specifications, the antenna switching between the transmission of the second gate of the interrogation signal s(t) and that of the third gate must be fast, i.e. it must be done in about some hundreds of nanoseconds ( less than 200 ns).
It is difficult and even impossible to implement an architecture of this kind for making fast ( less than 200 ns) power switches with a peak power of over 2 kW. Indeed, the transmission chain presently used in the making of high-power transmitters has a power switch 6v with a relatively low switching speed (with a switching time of about 1 xcexcs). This low switching speed is actually due to the fact that it is sought to have high-power transmitters. This is because the voltage handling capability of the PIN diodes of the switch is proportional to the thickness of their intrinsic region whereas their switching speed, which is related to the lifetime of the minority carriers, is inversely proportional to this thickness. Furthermore, the standard structure of IFF transmitters dictates the use of a circulator 5 between the amplification device 3 and the switch 6v owing to an infinite standing wave ratio (SWR) which entails the use of PIN diodes having a voltage handling capability that is twice the maximum value. This means that the switching speed is further reduced.
To overcome this drawback, the present invention, instead of using a switch placed downline, uses a low-power distribution encoder, placed upline with respect to the amplification, and a distribution decoder for the selection switching of the output channels.
To this end, an object of the invention is a method for the encoding of distribution comprising a step for the superposing, on a signal s(t), of a piece of distribution information i(t) used for the subsequent distribution of the total power Ps of said signal s(t), appearing at output of a system xcex93, to one or more outputs {Sxcex93} of said system xcex93.
This method is used by the distribution encoder comprising an element which:
receives a signal s(t),
receives a piece of distribution information i(t) used for the subsequent distribution of the total power Ps of said signal s(t) on said output or outputs {Sxcex93} of a system xcex93, and
superposes said piece of received distribution information i(t) on said received signal s(t).
In order to decode the distribution information, the invention also proposes a distribution decoding method comprising at least the following steps:
the reception of an encoded signal c(t) or a divided encoder signal (cj(t))jxcex5[1,2N] comprising a useful signal s(t) and a piece of distribution information i(t),
the sending of said signal s(t) to each of the outputs {Sxcex93} of a system xcex93 in distributing the total power Ps received at said outputs {Sxcex93} depending on said distribution information i(t).
This method is used by the distribution encoder comprising:
one or more inputs at which there is received an encoded signal c(t) or a divided encoded signal (cj(t))jxcex5[1,2N] comprising a useful signal s(t) and a piece of distribution information i(t) identically or differently for each signal,
several outputs connected to the outputs {Sxcex93} of a system xcex93 on which said signal s(t) is sent in distributing the total power received Ps depending on said piece of distribution information i(t).
The invention also proposes a transmission chain comprising at least the distribution encoder and the distribution decoder described here above.
The architecture thus obtained enables the switching of the power output by improving the following parameters:
the switching speed: the switching is done in less than 300 nanoseconds;
the power handling capability of the switching function; and
the standing wave ratio (SWR) capability of the switching function which becomes infinite.
This architecture also optimizes the power balance of a transmission chain by masking the switching function losses.
Furthermore, this architecture is less complex because it enables the use of components with standard specifications commonly used in the semiconductor industry.